Building glass is nearly invisible to most birds, and bird strikes against glass are usually fatal to the bird. Even if a bird initially recovers sufficiently to fly away after striking a window or other glass surface, it often will die later from internal hemorrhaging. Estimates of the number of avian deaths from glass strikes range from 100 million to one billion per year in North America. These collisions represent a leading cause of death to many bird populations, second only to habitat loss. Glass has many advantages as a green building material, and is likely to remain a popular choice of building materials in the coming years.